With recent advancement in scientific technology and medical technology, radiation-relevant equipment has been rapidly developed as diagnostic equipment and radiographic equipment has been generalized. An X-ray system is generally known as popularized diagnostic equipment which is radiation-relevant equipment. The X-ray system is used to visualize an anatomical structure and to detect a pathological phenomenon, disease, or an abnormal anatomical structure.
The X-ray system can be roughly classified into a film system, a computed radiography (CR) system, and a digital radiography (DR) system depending on an image acquiring scheme.
The film system is a most general imaging method for X-ray imaging. Here, X-rays passing through a subject form a latent image on a photosensitive film and the photosensitive film is developed by chemical treatment in a darkroom to visualize an image.
The CR system is a method of using an image plate (IP) cassette formed of cumulative fluorescent substance (or photostimulable fluorescent substance) instead of the photosensitive film in the film system. Here, X-rays passing through a subject is left in the form of transformed energy in the IP cassette and is stored as a latent image. Thereafter, when the IP cassette is inserted into an image reader and is irradiated with a laser beam, the IP cassette emits light depending on an amount of X-rays incident on the IP cassette and the image reader converts intensity of emitted light into electrical signals and converts the electrical signals into a digital image.
The DR system is classified into a camera system using a charge-coupled device (CCD) or the like and a panel system. The CCD system uses a CCD sensor and the CCD sensor is partitioned into very small cells which are called pixels. Electric intensity is determined depending on an amount of X-rays incident on each pixel and an electrical signal based thereon is digitalized by an analog-digital converter. The DR system does not need an image reader unlike the CR system and a digital image can be immediately acquired. The panel system includes plural photodetection pixels in a flat panel and each photodetection pixel senses X-rays. Each photodetection pixel senses X-rays which are generated from an X-ray generator and transmitted by a subject and outputs an electrical signal. The electrical signal is read out by a readout integrated circuit (ROIC).
An DR type X-ray system is more expensive than a film type or CR type X-ray system and thus is mainly used in large-scale hospitals and a CR type or film type X-rays system which is relatively cheap is used in small-scale hospitals.